#18,293
Earlier this month, in Australia : Biodiversity Council Webinar on HPAI H5 Avian Flu Threat, we looked at an informative webinar, held in late August by Australia's Biodiversity Council, on what they are doing to prepare for HPAI H5's expected arrival.
Australia isn't free from avian flu, as they have a wide variety of homegrown LPAI viruses (including H5 & H7), which occasionally spontaneously mutate into HPAI viruses in poultry (see Australia: 11th Avian H7 Outbreak, Now Reported in ACT).For now, Australia, New Zealand, and Oceania remain the only continental region on earth free of the HPAI H5Nx virus, which has now been spread via migratory birds to every other continent (see flyway map above).
Despite lying beneath both the West Pacific and East Asian–Australasian Flyway (see map below), Australia's wildlife (except when invasive species have been introduced by humans), has remained remarkably separate and distinct from the rest of the world.
This good fortune has often been attributed to the Wallace and Weber lines; imaginary dividing lines used to mark the difference between animal species found in Australia and Papua New Guinea and the rest of Southeast Asia (see 2008 study Will Wallace’s Line Save Australia from Avian Influenza?).
On the western side you'll find Elephants, monkeys, leopards, tigers, and water buffalo while on the eastern side, you'll mostly find marsupials (kangaroos, Koalas, wombats, etc.).
These stark faunal differences also extend to birds, reptiles, and even insects. Importantly for avian flu, very few migratory birds appear to cross the Wallace line (see The Australo-Papuan bird migration system: another consequence of Wallace's Line).
But this barrier isn't impenetrable.
- There were brief reports in 2007 of H5N1 being detected in poultry in both West Papua and the Maluku Islands; both of which lie on the Eastern side of the Wallace line.
- Perhaps more importantly, the range of bird species that now carry HPAI H5 has grown markedly over the past few years (see DEFRA: The Unprecedented `Order Shift' In Wild Bird H5N1 Positives In Europe & The UK), and now includes both Suliformes and Charadriiformes (shore birds).
- Some shore birds, such as the grey plover, have been tracked by satellite, and found to make a 9000 km non-stop flight from Adelaide to China, on their way to Siberia (link).
All of which brings us to a new study, by Michelle Wille (@duckswabber) et al., which presents evidence of recent incursions of both Eurasian and North American LPAI viruses into Australian birds. This is an accepted manuscript, published prior to final formatting.
Due to its length, I've only posted the link, abstract, and some brief excerpts. Follow the link to read it in its entirety. I'll have a brief postscript after the break.
Michelle Wille, Ivano Broz, Tanya Cherrington, Allison Crawley, Blaine Farrugia, Mark Ford, Melinda Frost, Joanne Grimsey, Peter D Kirkland, Shaylie Latimore ... Show moreVirus Evolution, veae076, https://doi.org/10.1093/ve/veae076Published: 10 September 2024 Article history
Abstract
The current panzootic of high pathogenicity avian influenza virus H5N1 demonstrates how viral incursions can have major ramifications for wildlife and domestic animals. Herein, we describe the recent incursion into Australia of two low pathogenicity avian influenza virus subtypes, H4 and H10, that exhibited contrasting evolutionary dynamics.
Viruses detected from national surveillance and disease investigations between 2020-2022 revealed 27 genomes, 24 of which have at least one segment more closely related to Eurasian or North American avian influenza lineages than those already circulating in Australia.
Phylogenetic analysis revealed that H4 viruses circulating in shorebirds represent a recent incursion from Asia that is distinct from those circulating concurrently in Australian waterfowl. Analysis of the internal segments further demonstrates exclusive, persistent circulation in shorebirds.
This contrasts with H10, where a novel lineage has emerged in wild waterfowl, poultry and captive birds across Australia, and has likely replaced previously circulating H10 lineages through competitive exclusion. Elucidating different dynamics for avian influenza incursions supports effective disease risk identification and communication that better informs disease preparedness and response.
(SNIP)
Discussion
We provide compelling evidence of shorebirds forming an important vector for intercontinental spread of avian influenza viruses between Asia and Australia and demonstrate key differences in the outcomes of viral introduction events resulting in contrasting opportunities for introduction, establishment, distribution and evolution of avian influenza viruses on the Australian continent.
(SNIP)
The understanding of viral incursion and consequent dispersal is of critical importance for both LPAIV and HPAIV. The global HPAIV H5N1 panzootic is affecting wildlife on all continents except Australia (Oceania) (Klaassen et al. 2023, Wille et al. 2024). A greater understanding of the rates and risk factors for viral incursion, establishment and spread across space, time and host community of LPAIV, such as presented here, may play a key role in informing risk assessment and responses strategies for potential HPAIV incursions.
Critically, our study highlights that shorebirds should be monitored for viral incursion, which will reveal whether the virus has established in the local waterfowl population (Wille et al. 2024).
Studies of viral movement within Australia (Wille et al. 2022), as well as the understanding of environmental factors on LPAIV virus ecology in waterfowl (Wille et al. 2023) and spillover risk to poultry (Ferenczi et al. 2021) are critical to response planning.
The history of HPAI H5's global expansion has been filled with unexpected milestones.
- For nearly two decades it was widely assumed that `sick' migratory birds could not cross the expanse of the Pacific, and introduce H5Nx to the United States/Canada. But that's exactly what happened in Dec 2014, an event which sparked the largest North American avian epizootic to that date.
- HPAI H5Nx had never been reported in the Southern Hemisphere either, until it unexpectedly crossed the African equator, and turned up in South Africa in the spring of 2017.
- In late 2021, HPAI H5 crossed both the Pacific and the Atlantic (see Multiple Introductions of H5 HPAI Viruses into Canada Via both East Asia-Australasia/Pacific & Atlantic Flyways), allowing the virus to spread throughout North and South America.
- And just 11 months ago, HPAI was confirmed to have reached Antarctica for the first time (see SGSSI Statement: HPAI Confirmed in Brown Skua Populations on Bird Island, South Georgia (Antarctica))
Given the evidence of recent incursion of LPAI H4 and H10 viruses into Australia by shorebirds - and HPAI H5's recent expansion into Suliformes and Charadriiformes - authorities there have good reason to suspect they could be the next stop on H5N1's world tour.
